Don't know about the blank sleeve one you've bought, and the only thing I remember about the blue covered one are some Delroy Wilson dubs - can't remember which ones exactly. I can ask a friend about the blue one, if so.

If I may,,,,not familiar with xray music - Are these reissues? If so, what's the pressing quality like? Did it say these are on the 'Presitge' label?

no I don't think it is a reissue, if you check this link and scroll down 2/3 of the page there is some more info. The LP contains the same tracks as the BAF reissue (except from the bonus tracks of course).
http://xraymusic.co.uk/kingtubby70s2.htmNo my copy is not on the Prestige label, and the pressing quality is nice.
The thing is that I saw the track list somewhere on the internet for the "blue album" (can't remeber where though), and it was totally different from the tracklist on the xraymusic-site if I remember it correct.

According to the sleevenotes on Yabby U's "King Tubby's Prophesy Of Dub" (http://www.bloodandfire.co.uk/cds/sleeves/bafcd005.pdf), the "Prophecies of Dub" LP is a completely different album issued in 1976 and mixed by Pat Kelly at King Tubby's (check page 2 on the link above).